One of the most familiar and frequently used hand tools is the screwdriver, a tool used for turning a variety of fastening devices such as different types of screws, bolts, nuts, etc.
Conventional screwdrivers typically consist of merely a handle adapted to be encircled by the fingers and palm of a user for gripping and rotating the screwdriver, and a shank connected to the handle for rotation therewith, the shank having a specifically shaped free end for engaging with a specifically shaped fastening device for turning the latter. Since there is a large variety of fastening devices available, for example, slot head screws, phillips head screws, hexagonal set screws, hexagonal head screws and various shaped nuts, as well as various sizes of each of the above, it is apparent that a large number of separate tools must be maintained on hand by a user in order for him to have the capability of installing or removing any one of the above mentioned fastening devices, as well as others not mentioned above, that listing being merely exemplary. For example, it would typically be necessary for a worker to have several sizes each of slot head screw drivers, phillips head screwdrivers, nut drivers, allen wrenches, etc., in order to be able to use any of these fastening devices at will. Obviously, such a collection of separate hand tools presents the problems of the expense incurred in obtaining them as well as the storage and carrying capability to have these tools available when and where they are needed.
Another problem frequently encountered with hand tools for turning fastening devices such as the tools mentioned above is that of the difficulty in applying sufficient force to the tool to do the job for which it is designed. This problem is particularly bothersome in the larger sizes of such tools, for example screwdrivers having shanks four to six inches long and approximately one quarter wide in diameter. It is not uncommon that such a screwdriver can withstand far more torque than can be applied to it by the users hand on the handle provided, either because the user's hand slips or the handle for lack of a proper gripping surface or because the gripping surface is poorly designed and causes pain when high torque is applied to it. This problem is compounded by the necessity, particularly in large turning tools, if applying a high longitudinal force to the tool as well as a high torque in order to keep the working end of the tool in proper engagement with the fastening device when the latter is presenting high resistance to turning, such as when inserting a screw into wood without first drilling a pilot hole, or removing a machine screw which has become rusted in place. Since the handles of conventional turning tools are generally cylindrical, it is difficult to apply a high longitudinal force simultaneously with a high torque without experiencing either loss of gripping capability, or pain to the hand or wrist, or both. It is especially hard on the wrist to grasp a conventional screwdriver handle and exert a high torque even with a good gripping surface while utilizing the other hand to push on the screwdriver to apply the longitudinal force required to keep the working end of the screwdriver in engagement with the fastening device.
Several attempts have been made to solve both of the above mentioned problems. While these attempts have met with some degree of success, they have not satisfactorily solved both problems. For example, screwdrivers have been made with interchangeable tool bits which removably attach to a single shank, so that it is not necessary to have a separate tool for all of the difficult types and sizes of fastening devices. It is, however, frequently difficult to insert and remove a tool bit with the standard C-ring or ball detent retaining means usually provided. Some have included storage facilities, such as hollow handles for storing a plurality of tool bits, but these have not been conveniently designed. Attempts have also been made to improve the gripping capability of screwdriver handles by providing various forms of directionally oriented ribs on the surface of the handle so that a greater gripping force can be exerted in one direction than in the other. In order to obtain the increased gripping force for turning this type of screwdriver in both directions, the screwdriver handle is made so that the shank is removable and can be connected to either end of the handle. Further, at least one screwdriver has a handle in the shape of a ball to facilitate applying a high longitudinal force simultaneously with a high torque, with tool bit storage compartments inside of the ball. All of these individual solutions have disadvantages and drawbacks to one extent or another, such as inconvenience in use, bulky size, excessive manufacturing expense, etc.
Thus, there is a need for a compound turning tool which avoids the disadvantages and drawbacks of the prior art tools yet, which confines the advantages of those tools into a single tool which is convenient to use, is not bulky and which can be manufactured at a cost which is competitive with the cost of known turning tools.